How to run python commands from flutter using tcp socket

Question

Im trying to send commands to a python script from flutter using tcp sockets. In python Im using the pyzmq library.

Python:

import time
import zmq

context = zmq.Context()
socket = context.socket(zmq.REP)
socket.bind("tcp://*:5556")

while True:
    #  Wait for next request from client
    print('Listening...')
    message = socket.recv()
    print("Received request: %s" % message)

    #  Do some 'work'
    time.sleep(1)

    #  Send reply back to client
    socket.send(b"World")

I then send messages to the python receiver using flutter but nothing is getting received or printed out in python. Simplified code below:

import 'dart:async';
import 'dart:convert';
import 'dart:io';

socket = await Socket.connect('localhost', 5556);
socket.add(utf8.encode('hello'));

How can I get this working?